In order to equip such aircraft, it is known that the air intake should not exhibit any drag, mass or bulk which are prohibitive. The air intake must finally be capable of ensuring a correct air supply to the engine or engines, throughout the flight envelope extending up to a high Mach number (about Mach 10 to 12).
The air intake must therefore be able to exhibit good performance, in terms of effectiveness and of throughput, over a large flight envelope, in order to be able to be applied to the abovementioned types of aircraft: for this reason, the air intake must be adapted to the Mach number and to the flight altitude, two parameters which are directly related.
In fact, low altitude flight can be envisaged only at moderate Mach numbers (up to 3), for reasons of temperature properties of materials, whereas at high altitude (20,000 to 30,000 meters), the Mach number has to be markedly greater in order, having regard to the rarefaction of the air, to allow sufficient dynamic pressure to be maintained to provide the lift and/or acceleration of the aircraft.
That being so, in order to obtain high thrust over the whole trajectory of the aircraft, both at low and at high altitude, it is necessary to supply the engine with a very variable throughput of combustion air with a total pressure recovery rate sufficient for all Mach numbers.
The air intake must therefore present an entry cross section which can increase in significant proportions with the increase in the Mach number: this increase in the inlet cross section must be able to carry on up to about Mach 6 or 7.
Variable geometry air inlets have therefore been proposed.
By the French Patent no. 2 635 075, in the name of the present Assignee, a variable-geometry, two-dimensional supersonic air intake is known including, on the one hand, a fairing and, on the other hand, a front flap forming a visor and articulated about a pivot pin situated opposite the fairing, as well as a movable fairing nose, situated in front of the fairing and integral with the front flap, this movable fairing nose being arranged to be displaced in front of the fairing when the front flap is displaced in the direction which increases the cross section of the air intake.
This embodiment, satisfactory up to a Mach number of the order of 4, exhibits the drawback, however, that the Mach range is limited by the significant fairing drag which it involves at very high Mach, greater than 4 or 5.
In order to avoid the drawback of the fairing drag, and in order further to increase the range of variation of the inlet cross section for the combustion air and of the compression ratio, the present Assignee, in French Patent no. 2 635 076, proposed a two-dimensional supersonic and hypersonic air intake, including two visor-forming front flaps, arranged symmetrically on either side of a longitudinal plane of the air intake, each front flap being movable about a pivot pin situated simultaneously in the vicinity of the wall of the air intake which extends the front flap in question, and in the vicinity of a first boundary layer bleed arranged in the said wall of the air intake which extends said front flap rearwards.
The inner walls of the flaps, that is to say the walls each of which is turned towards the other flap, are thus configured as compression ramps which are face to face and vertical under the fuselage and/or the wings of the aircraft.
However, if the adaptation Mach is high, the total deflection, distributed into equal parts between the two compression ramps and the plane of symmetry of the air intake, leads to a very intense shock on the latter, which limits the effectiveness of the air intake at high Mach.
In order to enhance this effectiveness at high Mach, by better distributing the compression over the plane of symmetry, French Patent no. 2 635 076 proposes embodiments which are all the more sophisticated the higher the Mach range to be covered, through the addition, to each front flap, of a movable rear flap linked to the front flap and downstream of the first boundary layer bleed, the rear extremity of this movable rear flap interacting with the front extremity of a movable inner wall element in order to define a second boundary layer bleed, or by configuring the rear part of the inner wall of each front flap, so that it is formed by two articulated wall elements, the first on the front flap in question and the second on the first wall element, the rear extremity of the second wall element interacting with the front extremity of a movable inner wall element in order to define the first boundary layer bleed, the position of which in the channel of the air intake can vary as a function of the Mach number.
However, these embodiments with enhanced effectiveness are of high mechanical complexity and of increased mass.
Moreover, significant shock/boundary layer interaction problems are posed, in the region of the flanks of the air intake, as well as problems of integrating several air intakes of this type under the fuselage of an aerobic space launcher, for example, especially to ensure suitable operation of the propulsion system as a whole in transonic regime (possible blocking of the flow between the engine nacelles).